It is known that switched-mode power supplies can be implemented with multiple outputs and using only one inductor for use as DC to DC converters. This saves on component count and reduces the numbers of pins required especially when an external compensation network is required for each converter.
A multiple output DC to DC converter is described by Woo et al in Load-Independent Control of Switching DC-DC Converters with Freewheeling Current Feedback by Young-Jin Woo, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 43, No. 12, December 2008, page 2798.
US patent application 2008/0231115A1 describes a multiple output DC-DC converter that can work in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM).
U.S. Pat. No. 7,432,614 B2 describes a single inductor multiple output switching DC-DC converter operating in pseudo-continuous conduction mode (PCCM) with freewheel switching. During a cycle of the multiple output switched mode supply, current is supplied to the inductor from a voltage source during one or more phases. Each of the multiple outputs is connected to the inductor during different phases of the cycle which may or may not by the same phases when the current is supplied to the inductor. Once an output has reached the required voltage the output is disconnected from the inductor and a next output is switched in to connect to the inductor. Once the final output has reached the required voltage then the inductor can be switched to free-wheel by a switch which can couple the two terminals of the inductor together until the beginning of the next cycle. The control of the current supplied to the inductor is done by a controller using sensors to determine the currents in the output loads, the switches and the inductor. The value of the sensed current can be used to modify the level of freewheel current.
A problem with multiple output DC to DC converters is the mutual influence of the outputs. Since all outputs share the same inductor, which has a limited amount of electrical energy, if one output has a load step and suddenly needs more energy, the other outputs will have less energy available. Another problem is determining which parameter or parameters the controller should use for input and what parameters to control. For converters operating in DCM mode, the control is simple, because the current in the inductor is allowed to return to zero or cross zero at the end of each cycle. However, in CCM mode the control is much more complex than DCM mode, because the current has to be maintained it a different value depending on the varying load requirements of the multiple outputs. It is therefore desirable to develop a simpler DC-to-DC converter for operation in CCM mode.